Synthesis of vitamin a



Patented Feb. 13, 1945 UNITED STATES PATENT OFFICE SYNTHESIS OF VITAMIN A Nicholas A. Miles, Belmont, Mass, asslgnor to Research Corporation, New York, N. Y., a corporation of New York No Drawing. Application March 3, 1942, Serial No. 433,229

8 Clalms. (01. 260-648) The general object the present invention is to provide a novel process for the synthetic production of vitamin A and a number of related intermediate products.

The accepted chemical structure of vitamin A is represented by the formula:

Cbmpoumi I EQUATION A ClCHiC OOCIH:

Other alkali alcoholates advantageously may be used in this condensation provided they are free from alcohols.

The reaction oi Equation A is understood to involve two reactions which proceed simultaneously or successively, i. e. the combination of the pionone and the ethyl chloroacetate forming the Compound Ila which reacts with the sodium ethylate yielding Compound II.

In the second step, Compound II is saponifled with 10% alcoholic potash and the resulting glycidie acid, Compound III, Equation 13, is separated and decarboxylated by distillation to produce 1-[2,6',6'-trimethyl cyclohexene-l'-yll-3- methyl butene-l-al-4, Compound IV, Equation C.

EQUATIONB 0H: CH:

CHI B H A: l] O dn+ KOH H G=C /CCO0H om im m Alcohol 0 Gimpound III Eons-non C CH: CH:

CH: H H J) H Distillation H C=C- -C=0+C0; Compound III+ H H CH:

Compound IV Compound IV may be prepared also by condensing, in an ethereal solution, p-ionone with ethyl dichloroacetate (ChCHCOOCzHs) in the presence of dilute magnesium amalgam, yielding Compound Ha, Equation D, which latter may be saponifled with alcoholic potash and the resulting saponiflcation produce decarboxylated to Product IV as in Equations B and C.

Eqtmrron D 0H: CH:

C Hi

ChCHCOOCiHi d-iouone-i- Mg-Hg Compound Ila Here it will be seen that Compound He is identical with the intermediate product of Equation A and when this Product H0 is subjected to saponiilcation with alcoholic KOH as in Equation B, it is simultaneously or successively converted into Compound II and Compound III.

Instead of decarboxylating Compound III by distillation as described above, Compound III is mixed with two molecular equivalents of pyridine and the resulting pyridine salt distilled under a pressure of about 1 mm. and the fraction distilling at about from C. to 103 0. (Compound We) collected. This fraction (Compound Iva) serves in the remainder of the process described hereinafter in the same way as Compound IV but evidence, such as its boiling point, spectroscopic examination, and absence of aldehydic properties, indicates that it is not Compound IV but a compound of the formula CH: CH:

\ CHI H K a B H C=C -CH 4 l H OH:

CompouMII/c In the third step, Compound IV or Compound Iva is condensed with sodium or lithium acetylide in a mixture of anhydrous ether and liquid ammonia at temperatures between -55 and -70 C. After the reaction is over, the ammonia is removed and the product treated with a dilute solution 01' tartaric acid, although aqueous solutions of ammonium sulfate, ammonium chloride or other organic acids may also be used. The resulting Compound V or Compound Va, Equations E and Ea, is extracted from this mixture in an impure state and maybe purified either by high vacuum distillation in an inert atmosphere or by preparing its phthalic acid ester by reacting the mixture with phthalic anhydrlde in pyridine solution. The phthalic acid ester is subsequently saponified to obtain the pure acetylene carbinols, Compound V or Compound Va.

It will be observed that Compounds V and Va are identical excepting that the positions of the hydrogen atom and the hydroxyl group on the third and fourth carbon atoms of the side chain counting from left to right are reversed.

Compound V or Compound Va may be prepared also (see Equation F) by the interaction of the mono-Grignard of acetylene (HCz-CMgX) and Compound IV or Compound IVa, respectively.

EQUATION F Compound IV HCECMgX or or Compound IVs (X stands for halogen) Compound Va In the fourth step, Compound V or Va may be dehydrated by distilling under high vacuum with small amounts of naphthalene sulfonic acid or p-toluene sulfonic acid yielding Compound VII directly (see Equation G).

EQUATION G Compound V vacuum Compound VII or b (see Equation 1) Compound Va distillation dehydrating catalysts Compound V Thus it will be seen that both Compounds IV and We may be treated in the same manner to yield Compound VII.

However, better yields of Compound VII are obtained by preparing from Compounds V and vs ill PX: H Compound V+ I D Pyridine H CH:

(in which X is a halogen) Cbmpoumi VI Eousrron Ha CH! CH:

(in which X is a halogen} Compound 'Vla It is observed that Equation Ha works best with the chloride, less well with the bromide, and poorly or not at all with the iodide.

EQUATION I OH: OH:

CHI

Compound VII Eouarron Ia KOH Compound Via 0 Compound VII alcohol Still another method of converting Compound V or Compound Va into Compound VII is to form the Grlgnard of Compound V havin the formula Grip'nurd of Compound V or the Grlgnard of Compound Va having the formula CHs CH:

CH: H H A} H H =c --1CICECMgX MgX H: CH:

(X stands for halogen) Grlpnurd of Compound V and mix either of said Grignard compounds with exactly one mol of In the fifth step the Grignard or alkali metal acetylide of Compound VII is prepared by allowtion J).

in: it to react in ether solution with ethyl magnesium bromide or metallic lithium, for example: To the Grisnard or alkali acstyiide oi Compound VII is slowly added methyl vinyl ketone (tiles) whereby the Product VIII is formed (see Equa- Enus'non J OH: OH:

H CH:

Compound VIII EQUATION K H: Compound VIII 4- Pdor action iron CH: CH:

CH: CH; H H J: H H H J: H C- =C-C= C=CH| H I OH:

Compound IX In the seventh step, Compound IX may be treated with acetic anhydrlde to form the acetic ester of vitamin. A, Compound XI, Equation L.

In this step any suitable acid anhydi'ide other than acetic anhydride, such as propionic and its higher homologues up to and includin palmitic and stearic and other organic acid anhydrides. such as benzoic acid anhydride, could be employed to produce the corresponding vitamin A esters, any of which may be converted into vitamin A by saponiflcation, as described hereinafter.

EQUATION L Com und XI acetic anhydride (see quation N) Compound IX Better yields of the acetate are obtained when Compound IX is treated first with a halogenating agent such as phosphorus tribromide in pyridine yielding Compound X. Equation M, which latter is treated with potassium acetate yielding Compound XI, Equation N.

In this step Compound IX may be treated with any other suitable halosenating agent such as phosphorus trichlorlde or thionyl chloride and the resulting halogen Compound X converted into any desired organic acid ester oi vitamin A by treatins it with the alkali metal salt of the desired acid in the presence of the free acid.

Still another method or making the esters of vitamin A is to treat Compound XV or Compound XVa with acetic or any other suitable organic acid anhydride in the presence of the alkali metal salt of said acid and heat the mixture in vacuum thienreby directly producing the acid ester of vitam A.

Equation M Compound IX+ Px' pyrldins (in which X stands [or 11 1 8 1 Cbmpound X Eons-non N Potssium acetate -O gentle heat CH1 CHI Compound X+ KYO HI I Compound XI The vitamin is finally prepared by saponiiying Compound XI, Equation 0, or by treating Compound X with silver hydroxide (see Equation P).

C a enemies-agar Equs'non O saponify alcoholic KOH 70 C. in N atmosphere EQUATION P A3011 Compound X+ o in alcoholic solution up to 0.

Compound XI+ Compound I Compound I In the preparation of Compound x1, the following alternative route may be used: Methyl vinyl ketone is condensed with sodium or lithium acetylide in liquid ammonia to produc Compound XII, Equation Q, which latter is then converted into the Grlgnard XIII, Equation R, by interaction with ethyl magnesium bromide. The Grignard XIII is allowed to react in ether solution with the Compound IV or We followed by bydrolysis with tartaric acid or ammonium sulfate to produce Compound XIV or XIVa, Equation S or Ba.

Eousrron Q CHI H t HsC=C- CECH Compound XII HCECNa EQUATION R CHI H & 1110:0- --CECMgX QCdIiMgX Compound XII-i- (X stands for halogen) Compound XIII Compound XIV or xIVa is then partially reduced to Compound XV or XVo using the catalysts and conditions described above (see Equations T and To) Eons-non '1 C dXIV+ H.

ompoun Pd on CoCOa or BaBOc CH; CH: c

H H H H H A H B C= C-H--C-C=C -C=CH:

t I H H Hy-CH:

. GmpouadXV EQUATIOITG C poundXIV+ H on o catalyst CH: CH:

OH: OH; H .H I! H H J H H C=C -g-C=C C=CH,

| i. a H CE:

I CompoundXVo An alternative method used to prepare Compound XIV or XIVa consists in the interaction of the Grignard of V or V0 with methyl vinylketone (see Equations U and Ho) EQUATION U Grignard of V CH; CH; CHI

(X stands [or halogen) Eom'rron Ua Grignard 0! Va CH: CH: CHO

(X stands for halogen) Compound XV or XVa is halogenated with a suitable agent such as a phosphorus trihalide,

dine at 0 C. yielding Compound XVI or XVlIo. Equations W and Wu, and the latter are dehydrohalogenated, for example. by treating with exactly one mol of potassium hydroxide in alcohol to yield Compound 1!. Equation Y.

Eammon W OH. OH; CH: CH1

1! H n n n a arm n c=c- -o-c=c- =c-cnx xv+ H idlnc at 0 OH:

(in which X stands ior halogen) Compound XVI Eqmrrou Wu CH: OH] CH] CH;

H n n H n n a r-x, H c=o- -c-c=c- =c-cnx xVo -e H Pyridine at 0 0 on.

(in which X stands (or halogen) (.bmpmnd XVIc (The above reactions work better with the chloride than with the bromide.)

EQUATION Y xv: x011 Compound X XVIo alcohol A more detailed account of the principal reactions is to be round in the following pages.

PREPARATION or GLYCID Esrsn Comrormo II, Fms'r Srnr, EQUATION A Twenty-four grams of metallic sodium is dissolved in about 300-400 cc. of absolute ethyl alcohol in a one liter filter flask fitted with a reflux condenser. It has been found preferable to add all 01 the sodium at once and after it had Bone into solution, the alcohol is removed under reduced pressure at temperatures ranging from Mill-170. A white sodium ethylate results. This is added slowly to a vigorously stirred mixture of 192 grams oi p-ionone, 122 grams ethyl chloroacetate and 110 cc. of anhydrous toluene (benzene may also be used) at 0. After all of the sodium ethylate had been added, stirring is continued until the mixture becomes homogeneous and brownish in color, then allowed to stand at room temperature for 7-10 hours. It is then heated on the water bath for 5 hours, cooled to room temperature and acidified with 25% acetic acid. The oil separating from this mixture is fractionated under reduced pressure and the fraction boiling at 152-155! (2-3 mm.) collected. A yield 01 about 80% 0! Compound II is obtained.

Pmluurron or Comeounns III sun IV, Suoonn S'rer, Eotmnons B AND C To obtain Compound III, 107 g. of Compound II is mixed with one equivalent (21.6 g.) of 10% alcoholic potash and the mixture heated on the water bath for about two hours. The alcohol is then removed under reduced pressure and the residue dissolved in the minimum amount of water and the aqueous mixture extracted a few times with ether to remove any unsaponiflable matter. The aqueous solution is then treated with 25% phosphoric acid and the oily layer which separates extracted with ether. The ether e. g. phosphorus trichloride or tribromide in pyri- 16 extract is then dried with anhydrous magnesium suliate. filtered and the ether removed under redueed pressure. The residue (Command III) is heated in an atmosphere of nitrogen and in the presence of powdered glass or finely divided copper to-i'acilitate the removal or carbon dioxide and the aldehyde formed finally fractionated under reduced pressure and the traction boiling at 143-145 mm.) collected. This has an a 1.5082 and forms a 2,4-dinitrophenylhydraaone: M. P. 155-157 having the correct combustion analysis.

This aldehyde (Compound IV) has also been prepared by the alternative method (Equation D) described as part or the second step.

The preparation of compound IVa from Compound III by reaction with pyridine and distillation has been suiliciently described above.

Synthesis of 1- [Z',6',6'-trimcthyl cyclohexenc-ryll -3-metlwl 3-apoc1 butane-1 (Compound Iva) Compound lVa To a mixture or 245 g. (2 mols) or ethyl chloroacetate and 110 g. 01' anhydrous, sulfur-free toluene contained in a three-necked, round-bottomed flask equipped with a mercury-sealed stirrer, a thermometer, and a calcium chloride tube and cooled to about -85' add 102 g. (1 mol) oi B-ionone. By means 01' a Gooch rubber connection introduce, over a period of two hours with rapid stirring, 46 g. (2 mols) ot finely powdered sodium ethoxide tree from alcohol. Bring the mixture slowly to room temperature by allowing it to stand overnight with moderate stirring in an atmosphere or nitrogen. Continue stirring while the mixture is heated in nitrogen on the water bath for four hours, then cool to room temperature and neutralize with a solution or 167 g. of glacial acetic acid in 500 cc. or water. The mixture separates into two layers. Remove the non-aqueous layer and extract the aqueous layer with two 50 cc. portions oi ether and combine the extracts with the non-aqueous layer. Remove the ether and the toluene and other low boiling constituents by subjecting the mixture to avacuum distillation (-20 mm.) in an atmosphere of nitrogen at the temperature of boiling water. Cool the residue (Compound 11) to room temperature and add to it 840 cc. of 95% alcohol containing 85 g. of potassium hydroxide and reflux the resulting mixture in nitrogen for one hour under a slightly reduced pressure, then remove under reduced pressure approximately two-thirds of the alcohol. Cool the residue and pour it into 1500 cc. oi deoxy enated water and extract the mixture successively with 500, 200 and 150 cc. of ether; combine the extracts and wash with 200 cc. of water and combine the latter with the aqueous solution. Add to the aqueous layer 200 cc. of fresh ether and acidity with 654 cc. oi 20% orthophosphoric acid. Remove ether layer and extract non-aqueous layer successively with 200 and 100 cc. of ether and combine ether extracts; wash ether extracts twice with 110 cc. portions or water, dry over anhydrous magnesium sulfate, filter and remove ether under reduced pressure. The residue consist of almost pure glycidic acid (Compound III) containing small amounts or ,e-ethoxy acetic acid.

To decarboxylate the glycidic acid dissolve it in 158 g. (2 mols) of pure anhydrous pyridine and subject the mixture to a vacuum distillation in an atmosphere of nitrogen. The pyridine comes over at lower temperatures, then, the residue is fractionated and the fraction boiling at 95-140 (2 mm.) is collected and designated as the crude portion or Compound-Iva. This prodnot is round to contain a small amount or an organic acid, and to remove the latter the prodnot is dissolved in 250 cc. of ether and the ethereal solution shaken vigorously twice with 200 cc. oi 5% sodium bicarbonate solution. The ethereal solution is then dried over magnesium sulfate, filtered, the ether removed under reduced pressure and the residue fractionated using a Claisen flask attached to a 30 cm. Vigreux column and the fraction boiling at -103 0-2 mm.) collected. n 1.5110, dis- 0.940. This product fails to give an aldehyde test with fuchsin reagent and absorption spectrum in the ultraviolet region of the spectrum fails to show the presence 01' an aldehyde group either insolated from or conjugated with the double bonds.

The large range in boiling point (90-103) indicates the presence in the product or the cis and trans isomers. The boiling point or the major isomer is about 99 to 103.

Piznriina'rroiv or Comotmns V AND VA, Tums S'rnr, EQUATIONS E AND EA To about 1 l. of liquid ammonia, in a 3-neclred flask equipped with a Hershberg stirrer and a dropping tunnel, was added 1 g. of hydrated ferric nitrate and l g. of metallic sodium and the mixture stirred for 1 hour while the temperature was kept at -55 to -'!0'. To this mixture was then added a trifle excess over half a mo] of metallic sodium and the mixture stirred for half an hour longer. Dry acetylene was then passed through the mixture for several hours or until most of the blue color had assumed a gray-white color. To this mixture was then added, in the course of three hours, 46 g. of Compound IV or Compound No in 200 cc. oi anhydrous ether taking care that the temperature or the mixture never rises above --60' and that the stirring is very rapid. After all of the aldehyde or oxide had been added, the mixture is stirred for 24 hours longer, keeping the temperature between 55 and -70. allowed to evaporate and the brownish residue treated with excess cold aqueous solution of d-tartaric acid and the resulting mixture extracted with ether from which the acetylene carbinol, Compound V or Compound Va. is isolated either by distillation under high vacuum (10" mm.) or by preparing its acid phthalate ester in anhydrou pyridine and subsequently saponifying this ester to obtain the pure acetylene carbinol. The phthaiic acid ester had the correct analysis and seml-micro-hydrogenation revealed the presence or 4 double bonds. The acetylene carbinol also gives a heavy whitish-gray precipitate with ammoniacal alcoholic silver nitrate solution characteristic for acetylenes.

Compounds V and Va have also been prepared, in anhydrous ether solution, by the interaction of Compounds IV and Na, with the mono-Grignard of acetylene (HCzCMgX), (Equation F).

PREPARATION or COMPOUNDS VI, VIA AND VII, FOURTH S'rnr, EQUATIONS H, Ha AND I AND Is Five g. of Compound V or Va is dissolved in about 15 g. of anhydrous pyridine and the mix- The ammonia is then ture cooled between and C. To this mixture is slowly added about 2.2 s. of Phosphorus tribromide or a corresponding amount of phosphorus triohloride taking care that the temperature does not rise above 0. After half an hour of standing at 0. the mixture i warmed to about 60-70" for 15 minutes, then, without separating Compound VI or Via, the mixture is treated with the calculated amount plus excess of 10% alcoholic potash. The mixture i heated on the water bath for half an hour, then poured in four times its volume of water. The aqueous mixture is then extracted several times with ether and the ethereal solution shaken a number of times with a solution of d-tartaric acid to remove the pyridine. Finally, the ether solution is dried over anhydrous magnesium sulfate, filtered, and the ether removed. The residue is nearly pure Compound VII, although for further purification one can distill it under a very high vacuum Compound VII may also be prepared by distilling Compound V Or Va under reduced pressure (10- -10" mm.) in the presence of small amounts, 1 to 5%, of p-toluene sulfonic acid or naphthalene sulfonic acid (Equation G).

Pnnranarrorr or Comromvn VIII, Firm-i S'rsr, EQUATION J Five g. of Compound VlI in 30 cc. of anhydrous ether is slowly added to an ethereal solution of the calculated amount of ethyl magnesium bromide and the mixture refluxed in an atmosphere of nitrogen for 5 to 10 hours. To this mixture is then slowly added at 0 with stirring about 2 8. of methyl vinyl ketone which is freshly distilled from small amounts or hydroquinone. The mixture is allowed to stand at room temperature overnight. then poured onto a mixture of ice and ammonium sulfate. After the Grignard mixture is completely hydrolyzed, the ethereal layer is separated and dried over anhydrous magnesium sulfate, filtered, and the ether removed under reduced pressure. The residue which is nearly pure Compound VIII may now be used for the next step.

For making Compound VIII from Compound VII via the alkali metal acetylide of Compound VII instead of the Grignard thereof, a mixture of equal parts of liquid ammonia and anhydrous ethyl ether is prepared and while being maintained at -60 to --'l0 C, small equivalent amounts of Compound VII dissolved in anhydrous ethyl ether and metallic lithium are added while rapidly stirring. After each addition, the blue color produced is permitted to completely disappear before another addition of Compound VII and lithium is made. After the desired amount of Compound VII and the equivalent amount of lithium have been dissolved, a solution of an equivalent quantity of methyl vinyl ketone in anhydrous ethyl ether is added dropwise, in the course of an hour, with continued stirring and while maintaining the temperature at 60 to '70 C. The stirring and maintenance of the temperature of 60 to 'l0 C. is then continued for about 10 hours. after which the temperature is allowed to rise and the ammonia to evaporate. The reaction mixture is then neutralized with tartaric acid dissolved in ice cold water and the resulting mixture extracted several times with ethyl ether. The combined ether extracts are dried with anhydrous magnesium sulfate. then filtered, the ether evaporated under reduced pressure and the residue subjected to a vacuum of from 10- to 10- mm. of mercury to vaporize and remove unreaeted Compound VII and methyl vinyl ketone. The residue 01 this last treatment, on analysis, conforms to the formula of Compound VIII.

PREPARATION or Comotmn IX, Srx'rn S'rsr, Eons-non K Compound VIII is dissolved in absolute alcohol and to the solution added about one-twentieth of the weight of Compound VIII of 1% palladium black deposited on solid powdered carbonate made in accordance with methods described in the literature. Barium sulfate may be advantageously used as the support of the catalyst. The calculated amount of hydrogen to saturate one of the bonds of the triple bond is then allowed to be absorbed by the system. The mixture is then filtered and the filtrate distilled under moderately reduced pressure. The residue is nearly pure Compound IX.

The reduction of Compound VIII to Compound IX may also be accomplished under 50-75 atmospheres of hydrogen at not higher than C. and in the presence or an active iron catalyst prepared by leaching the aluminum from an ironaluminum alloy (Equation K).

Pumas-non or Couromm XI, Ssvnrr-rn S'rar, EQUATIONS M AND N Although Compound X! may he prepared by the treatment of Compound IX with acetic anhydride (Equation L), better yields are obtained by dissolving Compound IX in anhydrous pyridine, cooling to 0, and adding the calculated amount of phosphorus tribromide, Equation M, taking care that the temperature does not rise above 0. The mixture is then warmed to room temperature and kept there for two hours. The mixture is then dissolved in ether and the ethereal solution extracted with a cold 25% solution of acetic acid to remove the pyridine and the phosphorous acid. After the ethereal solution is dried over anhydrous magnesium sulfate, and filtered, the ether is removed under reduced pressure and the residue Compound X, Equation M, is dissolved in glacial acetic acid and treated, in an atmosphere of nitrogen, with freshly fused potassium acetate, Equation N. The mixture is gently heated for about 2 hours to not higher than 100 C., then Poured in cold water and extracted with ether. The ethereal solution is separated, dried, and the ether removed. The residue contains considerable amount of Compound XI from which vitamin A can be easily prepared by saponii'ying it in the usual manner with alcoholic potash (Equation 0). However, Compound XI may be used directly as a vitamin A substitute.

This application is a continuation-in-part of my application Serial No. 353,775, filed August 22,1940.

I claim:

1. As a new product a compound of the formula H I H in which X stands for a halogen.

essence of vitamin A which comprises reacting a compound ottheiormule CH1 CHI CH: CHI 11 n J: n H n 1 n o=o- =o-o=oo=om with a halogenating compound and reacting the resulting compound with an alkali metal salt 01' a. cargoxylic acid in the presence of the carboxylic sci i 3. Process for the production of acetic acid ester of vitamin A which comprises reacting a compound of the i'ormula CH: CH:

l CH:

with a phosphorus halide and reacting the resultin: compound with an alkali acetate in the presence of acetic acid.

4. Process for the production or the hydrohslic acid ester 01' vitamin A which comprises reactin a compound of the formula.

5. Process for the production oi the hydro- 10 bromic acid ester of vitamin A which comprises reacting a compound 01 the iormula CHI CH;

HI CH: 11 n 4 n a E 11 l H withabrominating compound.

20 6. Process for the production of the hydrobromic acid ester of vitamin A which comprises reacting a compound of the formula cm onem on.

a El 11 n n L n 11 (2-0 =o-c=c- -c=cn.

r: em

with a phosphorus bromide.

NICHOLAS A. MILLS.

Certificate of Correction Patent No. 2,369,163.

February 13, 1945.

NICHOLAS A. MILAS It is hereby certified that error appears in the specification of the above numbered patent requiring correction as follows:

for that portion of the formula. reading on. 0 read O=CEs I age 6, second column, hne 68,

CHI & H

comx and that the said Letters Patent should be read with this correction therein that the some may co nform to the record of the case in the Peteht; Oflice.

signed and sealed this 26th day of June, A. D. 1945.

LESLIE FRAZER,

essence of vitamin A which comprises reacting a compound ottheiormule CH1 CHI CH: CHI 11 n J: n H n 1 n o=o- =o-o=oo=om with a halogenating compound and reacting the resulting compound with an alkali metal salt 01' a. cargoxylic acid in the presence of the carboxylic sci i 3. Process for the production of acetic acid ester of vitamin A which comprises reacting a compound of the i'ormula CH: CH:

l CH:

with a phosphorus halide and reacting the resultin: compound with an alkali acetate in the presence of acetic acid.

4. Process for the production or the hydrohslic acid ester 01' vitamin A which comprises reactin a compound of the formula.

5. Process for the production oi the hydro- 10 bromic acid ester of vitamin A which comprises reacting a compound 01 the iormula CHI CH;

HI CH: 11 n 4 n a E 11 l H withabrominating compound.

20 6. Process for the production of the hydrobromic acid ester of vitamin A which comprises reacting a compound of the formula cm onem on.

a El 11 n n L n 11 (2-0 =o-c=c- -c=cn.

r: em

with a phosphorus bromide.

NICHOLAS A. MILLS.

Certificate of Correction Patent No. 2,369,163.

February 13, 1945.

NICHOLAS A. MILAS It is hereby certified that error appears in the specification of the above numbered patent requiring correction as follows:

for that portion of the formula. reading on. 0 read O=CEs I age 6, second column, hne 68,

CHI & H

comx and that the said Letters Patent should be read with this correction therein that the some may co nform to the record of the case in the Peteht; Oflice.

signed and sealed this 26th day of June, A. D. 1945.

LESLIE FRAZER, 

